(i) Technical Field
The present invention relates to an image forming apparatus including a rotary developing device, and the rotary developing device.
(ii) Related Art
There are known image forming apparatuses each including a rotary developing device in which a plurality of developing units arranged around a rotation shaft are revolved around the rotation shaft to move a developing unit used for a current developing operation to a developing position. In some of such image forming apparatuses, a foreign-substance receiving plate is provided in a lower part of the rotary developing device to receive falling foreign substances, such as developer, falling from the rotary developing device.
In general, foreign metallic substances, such as spatter powder due to welding and screw chips, are often produced during production of an image forming apparatus. Although these foreign metallic substances are cleaned off during production, they are sometimes not sufficiently cleaned off, but remain in the image forming apparatus. Such remaining foreign metallic substances may fall owing to vibration occurring during transport and operation of the image forming apparatus.
In the image forming apparatus in which the above-described foreign-substance receiving plate is provided in the lower part of the rotary developing device, the above-described falling foreign metallic substrates are sometimes received by the foreign-substance receiving plate. Most developing units in the rotary developing device each include a developing roller having a magnet therein to transport developer containing magnetic carriers to a developing position while attracting the developer on a surface of the developing roller. For this reason, if foreign metallic substances are present on the foreign-substance receiving plate in the lower part of the rotary developing device, they are sometimes attached to the developing roller in the developing unit passing over the foreign-substance receiving plate and are carried together with the developer to the developing position. At the developing position, a surface of an image carrier for holding an electrostatic latent image to be developed opposes the developing roller in the developing unit. Hence, if the foreign metallic substances are attached to the developing roller, they may scrape the surface of the image carrier.